As is known, in currently available hard disks, dual-stage actuator systems for positioning of the read/write heads are provided. The first actuation stage generally comprises a supporting body (normally referred to as “E-block”, owing to the fact that, in side view, it is E-shaped), which is driven by a motor (also called “voice-coil motor”) and is equipped with arms to which a plurality of suspensions are fixed cantilevered. Each suspension is provided, at one of its free ends, with a joint or “gimbal”, formed starting from the suspension itself as a thin plate cut out on three and a half sides. Finally, on each gimbal a respective read/write (R/W) transducer (or “slider”) is carried, which, in use, is set facing one surface of a magnetic disk. The first actuation stage enables a coarse search to be carried out of the tracks to be read or written. In particular, the precision in the search depends upon the mechanical assembly forming the first actuation stage.
For each slider, the second actuation stage comprises a micro-actuator, normally of a rotary type, set between the slider itself and the gimbal. The micro-actuator is controlled by signals supplied by electronic control devices (not illustrated herein), set at a distance on cards located inside a hard disk casing, and enables a finer control of the position of the slider during tracking.
As is known, the micro-actuator comprises a fixed body (stator), which is bonded to the gimbal, and a mobile mass (rotor), to which the slider is fixed. The stator and the rotor, which are made of an adequately doped semiconductor material, are connected together so that they can move angularly by means of elastic elements (springs) and have a plurality of comb-fingered stator and rotor arms.
Clearly, it is very important to protect the micro-actuator during use, in order to prevent foreign bodies, such as dust or fragments of material which have come away from one of the disks, from penetrating between the stator and the rotor, thus damaging them. For this purpose, a known solution is providing protective structures (caps) for encapsulating the micro-actuator, as is described, for instance, in the European patent application No. EP-A-1122720, filed on Feb. 2, 2000 in the name of the present applicant, and incorporated by reference. According to the above patent application, a micro-actuator is made in a first wafer of semiconductor material, which is bonded to a second wafer of semiconductor material and houses driving circuits for the micro-actuator itself. The micro-actuator, and in particular, the rotor and stator arms, are made in a portion of the first wafer, which, after bonding, faces the second wafer and hence is not directly accessible from outside. Furthermore, the first wafer comprises an encapsulating structure, which surrounds the micro-actuator at the sides and on a side opposite to the second wafer.
The known solutions do, however, present some limits. In fact, even though the protection against intrusion of foreign bodies is satisfactory, the processes of fabrication of encapsulated microstructures are complex and involve execution of numerous working steps, which are not standard in microelectronics, with a consequent non-optimal yield. Known micro-actuators hence have a very high production cost. Furthermore, given that they have a complex structure, they are easily subject to failure both during fabrication and during use. It would, instead, be desirable to have micro-actuators with simpler structures,—that are, for example, more compact and also more reliable.